A 0.25-mol sample of a weak acid with an unknown Pka was combined with 10.0-mL of 3.00 M KOH, and the resulting solution was diluted to 1.500 L. The measured pH of the solution was 3.85. What is the pKa of the weak acid?

Answer : The value of of the weak acid is, 4.72

Explanation :

First we have to calculate the moles of KOH.

Now we have to calculate the value of of the weak acid.

The equilibrium chemical reaction is:

Initial moles     0.25     0.03        0

At eqm.    (0.25-0.03)   0.03      0.03

                     = 0.22

Using Henderson Hesselbach equation :

Now put all the given values in this expression, we get:

Therefore, the value of of the weak acid is, 4.72

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.

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